Surgical resection is a means of removing sections of highly vascular organs within the human or animal body, such as the liver or the spleen. When tissue is cut (divided or transected) small blood vessels called arterioles are damaged or ruptured. Initial bleeding is followed by a coagulation cascade where the blood is turned into a clot in an attempt to plug the bleeding point. During an operation, it is desirable for a patient to lose as little blood as possible, so various devices have been developed in an attempt to provide blood free cutting.
For example, the Hemostatix® Thermal Scalpel System (http://www.hemostatix.com) combines a sharp blade with a haemostatic system. The blade is coated with a plastic material and connected to a heating unit which controls the temperature of the blade. The intention is for the heated blade to cauterise the tissue as it is cut.
Other known devices that cut and stop bleeding at the same time do not use a blade. Some devices use radiofrequency (RF) energy to cut and/or coagulate tissue. Other devices (known as harmonic scalpels) uses a rapidly vibrating tip to cut tissue.
Vessel sealing and resection techniques involve the permanent occlusion of vessels, arteries or veins, with a diameter between 1 and 7 mm or greater. The pressure that the seal has to withstand is that of the pumping pressure of the heart.
Vessel sealing is normally a multi-stage process. In a first stage, external pressure may be applied to the vessel wall, to reduce mechanically the volume of tissue, and displace the tissues within the cell wall, so that internal and external vessel surfaces are brought close together. In a second stage, heat may be applied to denature collagen in the vessel walls to cause intermingling of the matrix structure of the inner and outer walls. A third stage of heating may be needed to fix this structure.
If a vessel is to be resected, three seals are normally provided, especially for larger vessels. Two of the seals may be located on the side of the resection location closest to the heart. The vessel is then resected (i.e. divided) with RF energy or a mechanical blade. Subsequent collagenesis causes new fibres to invade the denatured collagen, and the vessel ‘grows’ in the occluded position.
The method of cutting using RF energy operates using the principle that as an electric current passes through a tissue matrix (aided by the ionic contents of the cells), the impedance to the flow of electrons across the tissue generates heat. When a pure sine wave is applied to the tissue matrix, enough heat is generated within the cells to vaporise the water content of the tissue. There is thus a huge rise in the internal pressure of the cell, which pressure rise cannot be controlled by the cell membrane, resulting in the cell rupturing. When this occurs over a wide area it can be seen that tissue has been transected.
RF coagulation operates by applying a less efficient waveform to the tissue, whereby instead of being vaporised, the cell contents are heated to around 65° C. This dries out the tissue by desiccation and also denatures the proteins in the walls of vessels and the collagen that makes up the cell wall. Denaturing the proteins acts as a stimulus to the coagulation cascade, so clotting is enhanced. At the same time the collagen in the wall is denatured from a rod like molecule to a coil, which causes the vessel to contract and reduce in size, giving the clot an anchor point, and a smaller area to plug.
If you cut across a vessel, e.g. a veiniole, it bleeds, which then releases fibrinogen to start the coagulation cascade, i.e. heparin, factor 8, etc., with a network of fibrin catching cells, which then forms a soft plug that is invaded by blast cells which create new tissue.
WO 2008/044000 discloses surgical resection apparatus adapted to simultaneously cut and seal highly vascularised tissue, such as the liver or spleen. The apparatus comprising a source of microwave radiation that is coupled to a surgical instrument having an antenna associated with a blade for cutting biological tissue, wherein the antenna is arranged to controllably deliver microwave energy from the source to a region where the blade cuts through tissue. The microwave energy can coagulate blood to effectively seal off the blood flow at the cutting region. WO 2008/044000 suggests the use of high microwave frequencies (e.g. 10 GHz or higher), which offer a particular advantage over the use of known lower microwave frequency ablation systems and radiofrequency (RF) systems due to the limited depth of penetration of the energy by radiation and the ability to enable small sharp blade structures to radiate energy efficiently into the tissue to seal off blood flow by being able to produce uniform fields along the length of the blade whilst at the same time being capable of cutting through the tissue to remove sections of diseased or cancerous tissue.
U.S. Pat. No. 6,582,427 discloses an electrosurgery system arranged to generate both RF energy (typically having a frequency of 1 MHz) and microwave energy (typically having a frequency of 2.45 GHz) for selective operation in a cutting mode or a coagulation mode.